Patients identified as having non-A, non-B hepatitis will be followed as long as possible. Liver biopsy will be obtained when the SGPT is elevated for more than 6 months and then as indicated thereafter. Biopsy material will be saved for fluorescent studies when reagents for non-A, non-B hepatitis become available. All patients developing non-A, non-B hepatitis following open heart surgery will be followed with serial studies of SGPT to determine the incidence of chronic liver disease and to compare this incidence with those having type B hepatitis.